The cable company recently replaced my old gateway/wireless router. After the new gateway was installed (a "Touchstone TG1682G Telephony Gateway", if it matters), both Google and Amazon required additional verification before I could log in to my accounts on their websites. Google gave me a message that my device was unknown or could not be verified and required that I either provide a backup email or phone to receive a confirmation code before proceeding. Amazon required me to enter an emailed code. AOL didn't seem to notice or care.
But my actual device that I was using to connect to these websites has not changed. It is the same computer I have always used. My IP address probably changed with the new gateway, but the cable company has always assigned new IP addresses several times per year and it has never triggered a security lockout by Google or Amazon. Previously I would get the occasional e-mail notification that a sign-in was made on a new device (either "Linux" or "Windows" depending on which OS I was using), but nothing was ever triggered by getting a new IP. (see note*)
Based on my understanding of a similar question asked on Quora it would be highly irregular if my router hardware were known to websites.
What about the installation of a new gateway could trigger account lockout protocols for Google and Amazon? Does anyone know what might be going on here?
*Note: per the accepted answer, it seems that along with the new gateway, I was also assigned a much different IP address than any I've previously had. My previous IP addresses had always been in the range 73.xxx.xxx.xxx, but my new IP is in the range 67.xxx.xxx.xxx. I suppose this was different enough to be considered "suspicious activity" and triggered their account lockout protocols.